Transcript Host–Microbe Relationships and Dispersion of Microbes

Epidemiology
Molecular epidemiology, Microbial Ecology, Vector Ecology and Population
Biology
Tracking microorganisms through space
Spatial distribution of organisms may depend on:
• Geographic range
• Habitat specificity
• Host specificity
• Ecosystem specificity
• Site or tissue specificity
Microbes are everywhere
•
•
•
•
Microbes are found all over the world in virtually every habitat and in/on
most organisms as symbionts
Free living microbes may sometimes become opportunistic parasites
Humans’ non-specific defenses help to protect from these opportunists
Some microbes are specialized pathogens and have specific abilities and
requirements to cause infections
Transport and Transmission of microbes
• Abiotic routes, vehicles and fomites (indirect contact)
– Water
– Wind/thermal currents
– Food
– Other
• Biotic routes
– Host to host (Direct contact)
• Human to human
• Animal reservoir to human
– Vector
• Biological (blood or feces of vector)
• Mechanical (vector transports on body)
• Combination of biotic and abiotic
Microbes in Water
Microbes in Water
Contamination of Water
affects drinking and
recreational water
Food Borne Illnesses
• Fecal contamination of food
– From animals (E. coli, Salmonella etc…)
– From humans (hepatitis A etc…)
• Parasites in tissue of meat (helminthes etc…)
• Food spoilage or intoxication (Botulism, aflatoxins etc..)
Direct Contact Transmission
• Types of contact: Bites, scratches, sneezes, coughs,
sexual contact, physical contact, exposure to blood or
body fluids
• Direct contact with:
– With humans-examples include VDs (STDs), MRSA
– With animals – examples include rabies, ringworm
– With vehicles (blood, feces, body fluids etc…)
brucellosis, Q fever, Tularemia
Vector Transmission
• Vectors are usually arthropods
• Biological transmission by haematophagous vectors
(blood feeding vectors)
• Through saliva of vector
• ‘dirty needle’ transmission by vector’s proboscis
(rarely occurs)
• Through blood or feces of vector
• Accidental ingestion of vector
• Mechanical vectors (non blood feeding)
• On body of vector
• In feces of vector
• Accidental ingestions
Insects
Siphonaptera-fleas
Diptera-flies
Nematocera
Ceratopogonidae-no-see-ums, sand gnats
Culicidae-mosquitoes
Psychodidae-sand flies
Simuliidae-blackflies
Brachycera
Tabanidae-horse and deer flies
Cyclorrhapha
Muscidae-houseflies
Glossinidae-tetse flies
Hemiptera-bugs
Reduviidae-conenose (kissing) bugs
Cimicidae-bed bugs
Dictyoptera
Blattidae-roaches
Anoplura-sucking lice
Some Insect Vectors
Cone nose bug
Mosquito
Flea
Tsetse fly
Mites (including ticks)
Arachnida
Acari
Ixodidae-hard ticks
Argasidae-soft ticks
Laelapidae-hematophagous mites
Dermanyssidae-hematophagous mites
Demodicidae-follicle mites
Trombiculidae-chiggers
Sarcoptidae-scabies mites
Ticks
Ticks
•
•
Ticks are important vectors
Some species also cause tick paralysis
American dog tick
Lone star tick
Black legged tick (deer tick)
Examples of vector-borne diseases
Mosquitoes- malaria, hemorrhagic fevers, viral
encephalitis, filariasis
Black flies- river blindness
Sand flies- leishmaniasis, Oroya fever
Fleas-plague, maybe bartonellosis, some tapeworms
Lice- trench fever, epidemic typhus, relapsing fever
Deer flies- loaiasis
Conenose (kissing) bugs- Chaga’s disease
Tsetse flies- African sleeping sickness
Ticks- Lyme disease, ehrlichiosis, RMSF, hemorrhagic
fevers
Chiggers- scrub typhus
Copepods and other crustaceans- cholera, dracunculiasis
Reservoirs
• Reservoirs maintain the disease agent in nature
• Animals
• Vertebrates- deer, rodents, monkeys etc..
• Invertebrates- clams, crustaceans, insects
(remember, sometimes a vector can also be a
reservoir)
• Protists- some amoebas
• Water or soil- some free-living, infectious organisms
can reproduce outside of the host in water or soil
(otherwise water and soil are just vehicles)
Natural factors that affect distribution and abundance of diseasecausing organisms
•
•
•
•
•
•
•
•
Environmental changes
Individual host, vector or reservoir
Population of hosts, vectors or reservoirs
Microbial antagonism, competitive exclusion
Genetic changes in disease agent
Natural selection
Stochastic effects (e.g. drift, bottlenecks etc…)
Host health and immunity (e.g. stress)
Environment and Disease
Host availability and abundance
(including vectors and reservoirs)
E
Abiotic factors
(Weather)
Ecosystem balance
Anthropogenic and societal factors that influence disease
Environmental degradation
Poverty
Pollution
Education
Hygiene
Overcrowding
Studying Temporal Variation
•
•
•
The distribution and abundance of microorganisms may vary with time
Outbreaks of disease may occur periodically in relation to changes in the
environment, changes in hosts, genetic change in the microbe itself, or a
combination of factors
For example, each year, outbreaks of influenza result in about 30,000
deaths. However, the severity may differ over time as different strains
emerge
Hospitals and the spread of disease
•
•
•
•
•
•
Nosocomial infections occur in hospitals
Hospitals may contain more immunocompromised people, who are more
susceptible
Invasive procedures are conducted, creating portals of entry for pathogens
Many opportunistic pathogens
Frequent use of antibiotics and the potential spread of antibiotic resistance
genes
Misdiagnosis of disease especially emerging or obscure pathogens
Pathogens frequently causing nosocomial infections
•
•
•
•
•
•
•
•
•
•
Staphylococcus aureus and MRSA
Streptococcus spp.
Pseudomonas aeruginosa
Enterococcus spp.
Escherichia coli
Klebsiella spp.
Enterobacter spp.
Clostridium difficile
Candida albicans
Many others
Epidemiology and Infection Terminology
Acute- short-term infection with dramatic onset and rapid recovery (or death)
Chronic- long-term infection
Definitive host- host in which a parasite reaches sexual maturity
Endemic-naturally occurring in a particular area
Enzootic-presence of pathogen in particular area maintained by local reservoirs and vectors
Epidemic-presence of disease agent above normal infection prevalence
Epizootic-out break of enzootic pathogen
Etiology- cause of disease
Fomite-inanimate objects that can transmit pathogens between hosts
Incidence-the number of new host who become infected
Infectious dose- number of agents required to cause disease
Intensity- the number of parasites in a single host
Intermediate host- host in which parasite develops to some extent but not to sexual maturity
Microbial antagonism- competition between microbes which can lead to suppression of a particular
type of disease agent
Opportunistic Pathogen/parasite (phoront or commensal becomes parasitic)
Obligate Parasite (cannot live without host)
Pathogen- organism that causes disease
Pathogenicity- organisms ability to cause disease
Prevalence-the rate or frequency of an organism as a proportion or percent
Reservoir-host that maintains disease agent in nature
Resident- symbiont that remains in a host for a significant period of time
Sylvatic-exist normally in the wild, not in the human population
Transient- symbiont that is in a host temporarily
Transovarial transmission-vertical transmission-vector to offspring
Transstadial transmission-transmission of agent across life stages of vector
Vector- Organism that carries an agent from one host to another
Vehicle- inanimate source of pathogens
Virulence-degree of pathogenicity of an organism
Zoonosis-disease of animals that can be transmitted to humans
Suffixes -emia –presence of, -osis, -iasis, -itis - referring to disease state or condition of infection